1. Field of the Invention
This invention relates to electronic circuits and, more particularly, to communication channels that provide the means whereby a plurality of computers may communicate.
2. Description of the Prior Art
Before the discovery of speech, man used signs and gestures to communicate with other people. As civilization advanced, man's ability to communicate increased. He used drum beats, smoke signals, signal flags, light signals, etc., to convey his thoughts to other people. Thereafter, electrical communication systems were developed like the teletype wherein one electronic communication system under the control of an operator communicated with other electrical systems.
Man has also developed machines such as computers which can perform a sequence of calculations without human intervention.
Functionally described, the present electronic digital computer comprises four components: an arithmetic or computing unit, a high-speed internal storage unit, a control unit, and input-output devices to enable the outside world to communicate with the computer. The data and instructions that are contained within the computer are indistinguishable from each other. Both are represented by electronic circuitry or binary coded patterns that are affixed to some material.
In order to exploit the high operating speeds of digital computers, the digital computer contains built-in branching operations that enable the control unit of the computer to select alternate paths through the computer circuitry for the solution of the particular problem that is currently being processed.
In order to improve the calculating capability and the efficiency of the computer, the computer may be connected to one or more additional computers, enabling each computer to simultaneously solve different parts of the same problems. Thus, each individual computer communicated with the master computer that was controlling and organizing the operation of the plurality of computers that were being connected together. An interface unit was required to be connected between each individual computer to make the computers electrically compatible and to have them operate with each other in a synchronous or asynchronous manner.
The electrical signals that were outputted by any one of the computers were electrically weak and were not able to travel great distances. Thus, the computers had to be connected in relatively close proximity, thereby being in the same electrical cabinets or in the same room. If the computers were connected by a complicated technology that utilized telephone lines or the like, the resulting communications were very slow.
Most of the systems that were designed by the prior art to interconnect a pluraility of computers utilized electrical cables that were short in length and were customized to interconnect the particular computers. Therefore, the computer interconnection systems were designed for the particular communication of two or more computers that were being interconnected. If additional computers or peripheral equipment were required to be added to the system, extensive hardware modifications of the existing computer hardware system were required.
Thus, it was very difficult and costly to develop a high-speed communications channel between a plurality of computers, particularly if the computers were produced by different manufacturers. This is so because of the problems due to line noise, differences in logic levels, signal attenuation, spacial relationships of the computers and the extensive modification that would be required for the system that was going to enable a plurality of computers to communicate with each other.